The invention relates to aspiration of blood samples through an elastomeric septum from pressurized flow channels such as arterial lines.
Such aspiration has become an important method of blood sampling. In this sampling technique, a needle or cannula is inserted into the flow channel through the elastomeric septum, and blood is withdrawn into a blood collection device such as a syringe attached to the needle or cannula. The needle tip is thus inserted into the flow channel through the elastomeric septum, and blood is drawn into the syringe through the bore of the needle. The needle is then removed from flow channel and septum and the sample is transported to the lab for analysis.
One major problem which exists with this technique is that the elevated pressure within the flow channel is transmitted through the bore of the needle into the syringe. Since syringes and needles commonly have a small amount of dead air space within them, a bubble of air will be displaced into and trapped within the syringe when blood is drawn into the syringe through the needle. The transmitted pressure from the flow channel into the syringe through the needle bore can compress the air bubble when the needle bore is in fluid communication with the flow channel. When the needle is removed from the pressurized flow channel and the needle tip exits the septum, the bore of the needle is exposed to atmospheric pressure which may be substantially lower than the pressure within the syringe which has now been pressurized. The pressurized air bubble within the syringe expands rapidly upon the reduction of pressure at the opening of the bore of the needle near the needle tip thereby forcing blood out of the needle through the exposed opening. This rapid expansion of the bubble within the syringe therefore causes blood to spurt from the needle tip. This spurt of potentially infectious blood may strike the nurse or spray onto the bedsheets resulting in substantial blood exposure to hospital personnel.
Pending U.S. patent application Ser. No. 07/302,835 filed Jan. 27, 1989, describes a novel aspiration system comprising an aspirator receiver and blunt aspirator for use with a pressurized flow channel such as an arterial line. This design substantially reduces the risk of needlestick injury but is still subject to the blood spurting problem as described above. The present invention is an improved blood aspiration system and technique which is designed to eliminate the blood spurting problem.
Blood cannot spurt if the pressure in the syringe is relieved while the needle tip is occluded by the septum. Therefore, detecting and indicating when the tip is so occluded is very useful.
The blood aspiration system of this invention provides an occlusion indicator as well as an aspirator receiver means in fluid communication with a flow channel. The flow channel is connectable to a catheter in fluid communication with a blood vessel having an elevated internal fluid pressure. The system further includes a blood aspirator having a proximal and a distal end and a bore extending from the proximal end to an distal opening near the distal end. The occlusion indicator indicates when the aspirator is positioned within the septum such that distal opening of the bore of the aspirator is occluded.
In the preferred embodiment the aspirator receiver includes a housing having a passage extending from a proximal opening to an interface with the flow channel. The passage is occluded with an elastomeric septum having a perforation for receiving a blood aspirator which is preferably a needle having a blunt distal tip. The blunt needle has a bore extending from a proximal hub to an opening near the distal tip of the needle. The hub is preferably connectable to and may be permanently attached to a conventional syringe having a piston and internal chamber. The needle further includes means defining a space extending distally about the needle. The space defining means is preferably a cylindrical shroud sized to be received over the housing of the aspirator receiver. The shroud is connected to the needle and preferably extends beyond the needle tip.
A needle occlusion indication means indicates the position of the needle within the septum wherein the tip of the needle is occluded, and is preferably provided on the housing, but may be provided along the outer surface of the needle. In the preferred embodiment, the occlusion indicator means comprises a detent on the outer surface of the housing of the aspirator receiver and a corresponding detent on the inner surface of the shroud. The detents are specifically positioned such that withdrawal of a needle which has been received over the aspirator receiver is inhibited at a position wherein the distal opening of the needle bore is fully within the elastomeric septum and is occluded by the septum. This, therefore, provides a tactile indication that the needle tip is located at a position wherein the opening near the tip is occluded. At this point the nurse can stop withdrawing the needle and hold the shroud and needle in position while retracting the syringe piston. This will effectively decompress any trapped air within the chamber of the syringe. The nurse can then apply additional force to withdraw the shrouded needle completely from the septum.